Mammoths contributed to global warming with methane emissions

Mammoths helped to fill the atmosphere with methane and keep the Earth warm
more than 13,000 years ago, scientists believe.

10:00AM BST 24 May 2010

Together with other large plant-eating mammals that are now extinct, they released around 9.6 million tonnes of the gas each year, experts estimated.

When the ''megafauna'' disappeared there was a dramatic fall in atmospheric methane which may have altered the climate.

Analysis of gases trapped in ice cores suggests that the loss of animal emissions accounted for a large amount of the decline.

''The changes in methane concentration at this time seem to be unique,'' said the researchers, writing in the journal Nature Geoscience.

Methane is a powerful greenhouse gas. The scientists, led by Dr Felisa Smith from the University of New Mexico in the US, pointed out that a ''cold event'' hit the Earth at about the same time that methane levels plunged.

''Our calculation suggest that decreased methane emissions caused by the extinction of New World megafauna could have played a role..'' they wrote.

Around 13,400 years ago the Americas were heavily populated by large-bodied herbivores such as mammoths, camelids and ground sloths and had a richer array of animals than present-day Africa.

But by 11,500 years ago, around 80% of these big mammals had vanished forever.

Their disappearance, accounting for more than 114 lost species, came within 1,000 years of the arrival of humans in the New World.

Experts disagree on the extent to which human hunters and environmental changes were responsible for the extinction.